文档介绍：Superconductivity
One of the most elegant phenomenon and beautiful story in Condensed Matter Physics
封东来
超导体
有些金属和symmetry breaking
- Landau-Ginzburg: order parameter
1. pairing
superconducting gap
2. phase coherence
superfluid density
Two essential ingredients
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Classical Rigidity
From Steven M. Girvin, Indiana University
Boulder school 2000 lecture notes
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Generalized rigidity in superconductor
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
"Generalized Rigidity"
(Anderson, 1960's)
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Microscopic order produce rigidity
1934, Garter & Casmir "two-fluid' model
But Order-parameter is a complex one, not a scalar
It is the complex pair wave function (BCS 1957)
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Rigidity explains Meissner effect
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
BCS theory
e
+Z
+Z
+Z
+Z
e
PHONON MEDIATED PAIRING
Pairs of electrons: Cooper pairs
Tc~wph exp(-1/l)~M-1/2
El-ph coupling constant: l
Superconducting gap: D
Superconductivity: condensation of Cooper pairs
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Donglai Feng “Electronic Structure of Strongly Correlated Systems”
Superconductivity
2-electron
bound state
-k
k
Cooper Pair
spin-singlet pairing
Superconductivity can only
be seen on low energy scales
and needs high resolution!
Metallic Density of States
Superconducting Density of States
Classic low temperature superconductor
A.